System and methods for spinal fusion

ABSTRACT

A system and method for spinal fusion comprising a spinal fusion implant of non-bone construction releasably coupled to an insertion instrument dimensioned to introduce the spinal fusion implant into any of a variety of spinal target sites, in particular into the thoracic region of the spine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of Ser. No. 14/931,351, filed Nov. 3, 2015, which is a continuation of Ser. No. 14/193,886, filed Feb. 28, 2014 (now U.S. Pat. No. 9,186,261), which is a continuation of U.S. patent application Ser. No. 12/044,917, filed on Mar. 7, 2008 (now U.S. Pat. No. 8,673,005), which claims the benefit of priority from U.S. Provisional Patent Application Ser. No. 60/905,674, entitled “Systems and Methods for Spinal Fusion,” and filed on Mar. 7, 2007, the entire contents of these prior application being hereby expressly incorporated by reference into this disclosure as if set forth in its entirety herein.

BACKGROUND OF THE INVENTION

I. Field of the Invention The present invention relates generally to spinal surgery and, more particularly, to a system and method for spinal fusion comprising a spinal fusion implant of non-bone construction releasably coupled to an insertion instrument dimensioned to introduce the spinal fusion implant into the thoracic region of the spine.

II. Discussion of the Prior Art

Currently there are nearly 500,000 spine lumbar, thoracic and cervical fusion procedures performed each year in the United States. Such procedures are commonly performed to correct problems, such as chronic back or neck pain, which result from degenerated intervertebral discs or trauma. Generally, spinal fusion procedures involve removing some or the entire diseased or damaged disc, and inserting one or more intervertebral implants into the resulting disc space. Introducing the intervertebral implant serves to restore the height between adjacent vertebrae (“disc height”), which reduces if not eliminates neural impingement commonly associated with a damaged or diseased disc.

Autologous bone grafts are widely used as intervertebral implant for thoracic fusion. Autologous bone grafts are obtained by harvesting a section of bone from the iliac crest of the patient and thereafter implanting the article of autologous bone graft to effect fusion. While generally effective, the use of autologous bone grafts suffers certain drawbacks. A primary drawback is the morbidity associated with harvesting the autologous graft from the patient's iliac crest. Another related drawback is the added surgical time required to perform the bone-harvesting.

Allograft bone grafts have been employed with increased regularity in an effort to overcome the drawbacks of autologous bone grafts. Allograft bone grafts are harvested from cadaveric specimens, machined, and sterilized for implantation. While allograft bone grafts eliminate the morbidity associated with iliac crest bone harvesting, as well as decrease the overall surgical time, they still suffer certain drawbacks. A primary drawback is supply constraint, in that the tissue banks that process and produce allograft bone implants find it difficult to forecast allograft given the inherent challenges in forecasting the receipt of cadavers. Another related drawback is that it is difficult to manufacture the allograft with consistent shape and strength characteristics given the variation from cadaver to cadaver.

The present invention is directed at overcoming, or at least improving upon, the disadvantages of the prior art.

SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks of the prior art by providing a spinal fusion system and related methods involving the use of a spinal fusion implant of non-bone construction. The non-bone construction of the spinal fusion implant of the present invention overcomes the drawbacks of the prior art in that it is not supply limited (as with allograft) and does not require harvesting bone from the patient (as with autograft). The spinal fusion implant of the present invention may be comprised of any suitable non-bone composition, including but not limited to polymer compositions (e.g. poly-ether-ether-ketone (PEEK) and/or poly-ether-ketone-ketone (PEKK)), ceramic, metal or any combination of these materials.

The spinal fusion implant of the present invention may be provided in any number of suitable shapes and sizes depending upon the particular surgical procedure or need. The spinal fusion implant of the present invention may be dimensioned for use in the cervical and/or lumbar spine without departing from the scope of the present invention. For thoracic fusion, the spinal fusion implant of the present invention may be dimensioned, by way of example only, having a width ranging between 15 and 20 mm, a height ranging between 6 and 16 mm, and a length ranging between 20 and 45 mm.

The spinal fusion implant has a top surface, a bottom surface, an anterior side, a posterior side, a proximal side, and a distal side. The spinal fusion implant of the present invention may be provided in such a shape as to promote the proper kyphotic curvature of the spine. Such shape may be accomplished by varying the angle between the top and bottom contact surfaces of the spinal fusion implant to reflect the desired curvature for the vertebral bodies being fused.

The desired angle between said top and bottom surfaces may be accomplished by providing the anterior face of the implant with a greater height than the posterior face of the implant. Thus the top and bottom contact surfaces may not be parallel to one another, but rather they may be angled towards one another at the posterior end and angled away from one another at the anterior end.

The spinal fusion implant of the present invention may be provided with any number of additional features for promoting fusion, such as an aperture extending between the upper and lower vertebral bodies which allow a boney bridge to form through the spinal fusion implant of the present invention. Such fusion-promoting aperture may be dimensioned to receive any number of suitable osteoinductive agents, including but not limited to bone morphogenic protein (BMP) and bio-resorbable polymers, including but not limited to any of a variety of poly (D,L-lactide-co-glycolide) based polymers. The spinal fusion implant of the present invention is preferably equipped with one or more lateral openings which aid in visualization at the time of implantation and at subsequent clinical evaluations.

The spinal fusion implant of the present invention may be provided with any number of suitable anti-migration features to prevent the spinal fusion implant from migrating or moving from the disc space after implantation. Suitable anti-migration features may include, but are not necessarily limited to, angled teeth formed along the upper and/or lower surfaces of the spinal fusion implant and/or spike elements disposed partially within and partially outside the top and/or bottom surfaces of the spinal fusion implant. Such anti-migration features provide the additional benefit of increasing the overall surface area between the spinal fusion implant of the present invention and the adjacent vertebrae, which promotes overall bone fusion rates.

The spinal fusion implant of the present invention may be provided with any number of features for enhancing the visualization of the implant during and/or after implantation into a spinal target site. According to one aspect of the present invention, such visualization enhancement features may take the form of the spike elements used for anti-migration, which may be manufactured from any of a variety of suitable materials, including but not limited to a metal, ceramic, and/or polymer material, preferably having radiopaque characteristics. The spike elements may also take any of a variety of suitable shapes, including but not limited to a generally elongated element disposed within the implant such that the ends thereof extend generally perpendicularly from the top and/or bottom surfaces of the implant. The spike elements may each comprise a unitary element extending through upper and lower surfaces or, alternatively, each spike element may comprise a shorter element which only extends through a single surface (that is, does not extend through the entire height of the implant). In any event, when the spike elements are provided having radiodense characteristics and the implant is manufactured from a radiolucent material (such as, by way of example only, PEEK and/or PEKK), the spike elements will be readily observable under X-ray or fluoroscopy such that a surgeon may track the progress of the implant during implantation and/or the placement of the implant after implantation.

The spinal implant of the present invention may be introduced into a spinal target site through the use of any of a variety of suitable instruments having the capability to releasably engage the spinal implant. In a preferred embodiment, the insertion instrument permits quick, direct, accurate placement of the spinal implant of the present invention into the intervertebral space. According to one embodiment, the insertion instrument includes a threaded engagement element dimensioned to threadably engage into a receiving aperture formed in the spinal fusion implant of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein:

FIG. 1 is a perspective view of a spinal fusion system of the present invention, including a thoracic fusion implant releasably coupled to an insertion instrument, according to one embodiment of the present invention;

FIG. 2-4 is a perspective view of the thoracic fusion implant of FIG. 1, illustrating (among other things), a fusion aperture extending between top and bottom surfaces, a plurality of visualization apertures extending through the side walls, and a variety of anti-migration features, according to one embodiment of the present invention;

FIG. 5 is a top view of the thoracic fusion implant of FIG. 1, illustrating (among other things) the fusion aperture and the anti-migration features, according to one embodiment of the present invention;

FIG. 6 is a side view of the thoracic fusion implant of FIG. 1, illustrating (among other things) the visualization aperture, the anti-migration features, and a receiving aperture for releasably engaging the insertion instrument of FIG. 1, according to one embodiment of the present invention;

FIG. 7 is an end view of the thoracic fusion implant of FIG. 1, illustrating (among other things) the receiving aperture formed in the proximal end and the anti-migration features, according to one embodiment of the present invention;

FIG. 8 is an end view of the thoracic fusion implant of FIG. 1, illustrating the distal end and the anti-migration features, according to one embodiment of the present invention;

FIG. 9 is a perspective view of the insertion instrument of FIG. 1 in a fully assembled form, according to one embodiment of the present invention;

FIG. 10 is an enlarged perspective view of the distal region of the insertion instrument of FIG. 1, according to one embodiment of the present invention;

FIG. 11 is a perspective exploded view of the insertion instrument of FIG. 1, illustrating the component parts of the insertion instrument according to one embodiment of the present invention; and

FIG. 12 represents a flourographic image of the implant and is a side view illustrating the “enhanced visualization” feature of the present invention as employed within a thoracic fusion implant according, to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The fusion implant system disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination.

FIG. 1 illustrates, by way of example only, a spinal fusion system 5 for performing spinal fusion between adjacent thoracic vertebrae, including an exemplary spinal fusion implant 10 and an exemplary insertion instrument 20 provided in accordance with the present invention. The spinal fusion implant 10 may be comprised of any suitable non-bone composition having suitable radiolucent characteristics, including but not limited to polymer compositions (e.g. poly-ether-ether-ketone (PEEK) and/or poly-ether-ketone-ketone (PEKK)) or any combination of PEEK and PEKK. The spinal fusion implant 10 of the present invention may be dimensioned, by way of example only, having a width ranging between 15 and 20 mm, a height ranging between 6 and 16 mm, and a length ranging between 20 and 45 mm.

As will be described in detail below, the insertion instrument 20 is configured to releasably maintain the exemplary spinal fusion implant 10 in the proper orientation during insertion into a thoracic disc space and thereafter release to deposit the implant 10. The exemplary spinal fusion implant 10, having been deposited in the disc space, facilitates spinal fusion restoring and maintaining a desired disc height as natural bone growth occurs through and/or past the implant 10, resulting in the formation of a boney bridge extending between the adjacent vertebral bodies. The implant 10 is particularly suited for introduction into the disc space via a lateral (trans-psoas) approach to the spine, but may be introduced in any of a variety of approaches, such as posterior, anterior, antero-lateral, and postero-lateral, without departing from the scope of the present invention (depending upon the sizing of the implant 10).

FIGS. 2-8 depict an example embodiment of the spinal fusion implant 10. The spinal fusion implant 10 has a top surface 31, a bottom surface 33, an anterior side 52, a posterior side 14, a proximal side 22, and a distal side 16. The generally D-shaped circumference of implant 10, shown by way of example only, is configured for placement in the thoracic spine. Preferably the anterior side 52 is dimensioned with a length than that of the posterior side 14. This may be accomplished, by way of example, by providing a large radius of curvature of the corners between the anterior side 52 and the distal and proximal ends 16 and 22, by angling the distal and proximal ends 16 and 22 such that they converge towards each other proximate the anterior side 52, or a combination of both. By way of example only the radius of the corners proximate the anterior side 52 may be approximately 0.25 inch (¼ inch) while the radius of the corners proximate the posterior side 14 may be approximately 0.06 inch ( 1/16 inch). Optionally, to promote the natural kyphotic curvature of the thoracic region of the spine, the posterior side 14 may be dimensioned at a height greater than that of the anterior side 52. This dimensioning allows for the upper 31 and lower surfaces 33 to converge toward one another at the anterior end, thereby forcing the fusing vertebrae to conform to the proper kyphotic curvature. The kyphotic curvature requirements may vary by patient, but the implant angle will likely lie in the range between 1° and 20°, with one example embodiment having and angle of 10°. In one embodiment, the top and bottom surfaces 31, 33 are generally flat across. However, it can be appreciated by one skilled in the art that the top and bottom surfaces 31, 33 may be provided in any number of suitable shapes, including but not limited to concave and/or convex. When provided as convex shapes, the top and bottom surfaces 31, 33 may better match the natural contours of the vertebral end plates.

The exemplary spinal fusion implant 10 also preferably includes anti-migration features designed to increase the friction between the spinal fusion implant 10 and the adjacent contacting surfaces of the vertebral bodies so as to prohibit migration of the spinal fusion implant 10 after implantation. Such anti-migration features may include ridges 6 provided along the top surface 31 and/or bottom surface 33. Additional anti-migration features may also include a spike element 7 disposed within the proximal region of the implant 10, a spike element 8 disposed within the distal region of the implant 10, and a pair of spike elements 9 disposed within the central region of the implant 10, one on the posterior side 14 and one on the anterior side 52. Thus, in a preferred embodiment, posterior side 14 is imbued with 3 spike elements 7, 8, 9, situated one at each end and the center, while the anterior side 52 is situated with a single spike element, situated near the center. This triangular arrangement of spike elements 7, 8, 9, is adopted for placement in the thoracic spine where the anterior portion of the vertebral body narrows sharply and is in clear proximity to the great vessels. Spike elements 7, 8, 9 may extend from the top surface 31 and/or bottom surface 33 within the respective proximal, distal and central regions of the implant 10. The spike elements 7, 8, 9 may be manufactured from any of a variety of suitable materials, including but not limited to a metal, ceramic, and/or polymer material, preferably having radiopaque characteristics. The spike elements 7, 8, 9 may also take any of a variety of suitable shapes, including but not limited to a generally elongated element disposed within the implant 10 such that the ends thereof extend generally perpendicularly from the upper and/or lower surfaces 31, 33 of the implant 10. As best appreciated in FIGS. 6-8, the spike elements 7, 8, 9 may each comprise a unitary element extending through top and bottom surfaces 31, 33. Alternatively, each spike element 7, 8, 9 may comprise a shorter element which only extends through a single surface 31, 33 (that is, does not extend through the entire height of the implant 10). In any event, when the spike elements 7, 8, 9 are provided having radiodense characteristics and the implant 10 is manufactured from a radiolucent material (such as, by way of example only, PEEK and/or PEKK), the spike elements 7, 8, 9 will be readily observable under X-ray or fluoroscopy such that a surgeon may track the progress of the implant 10 during implantation and/or the placement of the implant 10 after implantation.

The spinal fusion implant 10 of the present invention may be provided with any number of additional features for promoting fusion, such as an aperture 2 extending between the upper and lower vertebral bodies which allow a boney bridge to form through the spinal fusion implant 10. According to a still further aspect of the present invention, this fusion may be facilitated or augmented by introducing or positioning various osteoinductive materials within aperture 2 and/or adjacent to the spinal fusion implant 10. Such osteoinductive materials may be introduced before, during, or after the insertion of the exemplary spinal fusion implant 10, and may include (but are not necessarily limited to) autologous bone harvested from the patient receiving the spinal fusion implant 10, bone allograft, bone xenograft, any number of non-bone implants (e.g. ceramic, metallic, polymer), bone morphogenic protein, and bio-resorbable compositions, including but not limited to any of a variety of poly (D,L-lactide-co-glycolide) based polymers. The large fusion aperture 2 of the implant 10 may be provided in any of a variety of suitable shapes, including but not limited to the generally hourglass shape best viewed in FIG. 5, or a generally, rectangular, circular, oblong and/or triangular shape or any combination thereof. The preferred hourglass shape, shown in FIG. 5, maximizes the open area for boney growth through the implant 10 while still providing added support and contact surface area along the ends and enter of the implant.

The spinal fusion implant 10 of the present invention is preferably equipped with one or more visualization apertures 4 situated along the anterior 14 and posterior 52 sides, which aid in visualization at the time of implantation and at subsequent clinical evaluations. The plurality of visualization apertures 4 will allow a clinician to make visual observations of the degree of bony fusion un-obscured by the anterior 14 or posterior sides 52. Specifically, based on the generally radiolucent nature of the implant 10, the visualization apertures 4 provide the ability to visualize the interior of the implant 10 during X-ray and/or other suitable imaging techniques which are undertaken from the side (or “lateral”) perspective of the implant 10 (e.g. images taken from anterior/posterior position where the implant is inserted in a preferred position from a lateral approach). If fusion has taken place, the visualization apertures 4 will provide a method for the surgeon to make follow up assessments as to the degree of fusion without any visual interference from the spinal fusion implant 10. Further, the visualization apertures 4 will provide an avenue for cellular migration to the exterior of the spinal fusion implant 10. Thus, the spinal fusion implant 10 will serve as additional scaffolding for bone fusion on the exterior of the spinal fusion implant 10. The visualization apertures 4 may be provided in any of a variety of suitable shapes, including but not limited to the generally oblong shape best viewed in FIG. 6, or a generally circular, rectangular and/or triangular shape or any combination thereof.

The spinal fusion implant 10 may be provided with any number of suitable features for engaging the insertion instrument 20 without departing from the scope of the present invention. As best viewed in FIG. 7, one engagement mechanism involves providing a threaded receiving aperture 12 in the proximal sidewall 22 of the spinal fusion implant 10 of the present invention. The threaded receiving aperture 12 is dimensioned to threadably receive a threaded connector 24 on the insertion instrument 20 (as will be described in greater detail below). The receiving aperture 12 extends inwardly from the proximal side 22 in a generally perpendicular fashion relative to the proximal side 22. Although shown as having a generally circular cross-section, it will be appreciated that the receiving aperture 12 may be provided having any number of suitable shapes or cross-sections, including but not limited to rectangular or triangular. In addition to the receiving aperture 12, the spinal fusion implant 10 is preferably equipped with a pair of grooved purchase regions 60, 61 extending generally horizontally from either side of the receiving aperture 12. The grooved purchase regions 60, 61 are dimensioned to receive corresponding distal head ridges 62, 63 on the insertion instrument 20 (as will be described in greater detail below), which collectively provide an enhanced engagement between the implant 10 and the insertion instrument 20.

FIGS. 9-11 detail the exemplary insertion instrument 20 according to one embodiment of the invention. The exemplary insertion instrument 20 includes an elongated tubular element 28 and an inserter shaft 44. The elongated tubular element 28 is constructed with a distal head 26 at its distal end, distal head ridges 62, 63 on the distal end of the distal head 26, a thumbwheel housing 38 at its proximal end and a handle 42 at its proximal end. The elongated tubular element 28 is generally cylindrical and of a length sufficient to allow the device to span from the surgical target site to a location sufficiently outside the patient's body so the handle 42 and the thumbwheel housing 38 can be easily accessed by a clinician or a complimentary controlling device.

The elongated tubular element 28 is dimensioned to receive a spring 46 and the proximal end of the inserter shaft 44 into the inner bore 64 of the elongated tubular element 28. The inserter shaft 44 is dimensioned such that the threaded connector 24 at the distal end of the inserter shaft 44 just protrudes past the distal head ridges 62, 63 to allow engagement with the receiving aperture 12 of the spinal fusion implant 10. It should be appreciated by one skilled in the art that such a construction allows the inserter shaft 44 to be able to rotate freely within the elongated tubular element 28 while stabilized by the spring 46 to reduce any slidable play in the insertion instrument 20.

The handle 42 is generally disposed at the proximal end of the insertion instrument 20. The handle 42 is fixed to the thumbwheel housing 38 allowing easy handling by the clinician. Because the handle 42 is fixed the clinician has easy access to the thumbwheel 34 and can stably turn the thumbwheel 34 relative to the thumbwheel housing 38. Additionally, the relative orientation of the thumbwheel housing 38 to the handle 42 orients the clinician with respect to the distal head 26 and distal head ridge 62. By way of example, the thumbwheel housing 38 holds a thumbwheel 34, a set screw 32, and a spacer 36. The inserter shaft 44 is attached to the thumbwheel 34 and is freely rotatable with low friction due to the spacer 36. One skilled in the art can appreciate myriad methods of assembling a housing similar to the above described.

The distal head ridges 62, 63 are dimensioned to fit slidably into the purchase regions 60, 61 with low friction to allow accurate engagement of the threaded connector 24 to the receiving aperture 12 of the spinal fusion implant 10. In the presented embodiment, the outer dimension of the threaded connector 24 is smaller than the largest outer dimension of the distal head 26 and elongated tubular element 28. Alternatively, other methods of creating a gripping surface are contemplated including but not limited to knurling or facets.

In order to use the system to perform a spinal fusion procedure, the clinician must first designate the appropriate implant size (and optionally, angulation). After the spinal fusion implant 10 is chosen, the distal head ridges 62, 63 of the inserter shaft 44 are inserted into the purchase regions 60, 61 of the spinal fusion implant 10. At that time the spinal fusion implant 10 and insertion instrument 20 are slidably engaged with one another. Before the clinician can manipulate the combined spinal fusion implant 10 and insertion instrument 20, they must be releasably secured together. In order to secure the spinal fusion implant 10 onto the threaded connector 24 of the inserter instrument 20, the clinician employs the thumbwheel 34 to rotate the inserter shaft 44 and threaded connector 24. The rotation of the threaded connector 24 will releasably engage the receiving aperture 12 of the spinal fusion implant 10 and stabilize the insertion instrument 20 relative to the spinal fusion implant 10.

A clinician can utilize the secured system in either an open or minimally invasive spinal fusion procedure. In either type of procedure, a working channel is created in a patient that reaches the targeted spinal level. After the creation of that channel, the intervertebral space may be prepared via any number of well known preparation tools, including but not limited to kerrisons, rongeurs, pituitaries, and rasps. After preparation, the insertion instrument 20 is used to place a spinal fusion implant 10 into the prepared intervertebral space. Once the implant 10 is inserted into the prepared space, the implant 10 is released from the insertion instrument 20 by rotating the thumbwheel 34 to disengage the threaded connector 24 from the receiving aperture 12. This motion removes the compressive force on the purchase regions 60, 61 between the distal head 26 and the distal head ridges 62, 63 of the spinal fusion implant 10 and allows the insertion instrument to be slidably removed from the implant 10. After the threaded connector 24 is disengaged from the implant 10, the insertion instrument 20 is removed from the working channel and the channel is closed. As previously mentioned, additional materials may be included in the procedure before, during or after the insertion of the spinal fusion implant 10 to aid the natural fusion of the targeted spinal level.

The enhanced visualization features of the implant 10 is explained in greater detail with reference to FIG. 12, illustrating the implant 10 dimensioned particularly for use in a lateral approach having (by way of example only) a width ranging between 15 and 20 mm, a height ranging between 6 and 16 mm, and a length ranging between 20 and 45 mm. Furthermore, FIG. 12 illustrates the implant 10 from a side perspective clearly showing the location of the spike elements 7, 8, 9 relative to the implant 10 and the visualization apertures 4.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

For example, while described herein primarily with reference to the thoracic spinal surgery, it is to be readily appreciated that the spinal fusion implants of the present invention may be suitable for accomplishing fusion in the cervical or lumbar spine without departing from the scope of the present invention. It should be noted that implants designed for the cervical and lumbar regions may be composed in a similar manner, but having a lordosis-promoting shape, rather than the kyphosis promoting shape described above. Specifically, the anterior side may be dimensioned to have a height greater than the posterior side. Those implants 10 designed to be inserted into the cervical region may be very similar to those to be inserted into the thoracic region, albeit smaller, while those designed for the lumbar region may be larger. Moreover, it is to be readily appreciated that the insertion tools described herein may be employed with implants of any number of suitable constructions, including but not limited to metal, ceramic, plastic or composite.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined herein. 

What is claimed is:
 1. A spinal fusion implant configured to be positioned in an interbody space between a first vertebra and a second vertebra, comprising: a proximal wall, a distal wall, an anterior wall and a posterior wall, the anterior wall having a first length and being configured to face an anatomically anterior aspect of the interbody space while the implant is positioned in the interbody space, the posterior wall having a second length and being configured to face an anatomically posterior aspect of the interbody space while the implant is positioned in the interbody space, the anterior wall meeting the distal wall at a first corner having a first corner radius of curvature and meeting the proximal wall at a second corner having a second corner radius of curvature, the posterior wall meeting the distal wall at a third corner having a third corner radius of curvature and meeting the proximal wall at a fourth corner having a fourth corner radius of curvature, the first corner radius of curvature and the second corner radius of curvature being greater than the third corner radius of curvature and the fourth corner radius of curvature to provide a D-shaped circumference formed by the proximal wall, the distal wall, the anterior wall and the posterior wall; an upper surface of the implant comprising upper surfaces of the proximal wall, the distal wall, the anterior wall and the posterior wall, the upper surface comprising a first anti-migration feature configured to be in contact with the first vertebra while the implant is positioned in the interbody space; a lower surface of the implant comprising lower surfaces of the proximal wall, distal wall, anterior wall and posterior wall, the lower surface comprising a second anti-migration feature configured to be in contact with the second vertebra while the implant is positioned in the interbody space; a fusion aperture extending through an entire height of the implant extending from the upper surface of the implant to the lower surface of the implant to permit bone growth therein between the first vertebra and the second vertebra while the implant is positioned in the interbody space; and a first visualization aperture in the anterior wall and a second visualization aperture in the posterior wall, the first visualization aperture and the second visualization aperture in communication with the fusion aperture, the first and second visualization apertures configured to aid in visualization of bony fusion between the first and second vertebrae.
 2. The implant of claim 1, further comprising at least a portion of a radiopaque marker within at least one of the proximal wall, the distal wall, the anterior wall, and the posterior wall.
 3. The implant of claim 1, further comprising a first radiopaque marker, a second radiopaque marker, and a third radiopaque marker, the first radiopaque marker comprising at least a portion in the proximal wall, the second radiopaque marker comprising at least a portion in the distal wall, and the third radiopaque marker comprising at least a portion in the anterior wall or the posterior wall.
 4. The implant of claim 3, wherein the at least a portion of the third radiopaque marker is in a medial plane of the implant.
 5. The implant of claim 1, wherein the fusion aperture comprises an hourglass shape.
 6. The implant of claim 1, wherein four visualization apertures are on each of the anterior wall and the posterior wall, and wherein all of the visualization apertures are in communication with the fusion aperture.
 7. The implant of claim 6, wherein the four visualization apertures each comprise an oblong shape.
 8. The implant of claim 1, wherein the proximal wall comprises a threaded tool engagement aperture configured to receive a corresponding portion of an insertion tool for delivering the implant to a target position in the interbody space.
 9. The implant of claim 8, wherein the proximal wall further comprises a pair of lateral grooves configured to receive another corresponding portion of the insertion tool, the pair of lateral grooves extending horizontally in opposing directions from the threaded tool engagement aperture.
 10. The implant of claim 1, further comprising a spike element comprising at least a portion disposed within the proximal wall or the distal wall, the spike element comprising a portion protruding from an upper surface of the proximal wall or the distal wall and configured to be in contact with the first vertebra while the implant is positioned in the interbody space.
 11. The implant of claim 10, wherein the spike element comprises a radiopaque material.
 12. The implant of claim 1, further comprising a first spike element comprising a portion protruding from an upper surface of the distal wall, and another portion disposed within the distal wall, a second spike comprising a portion protruding from an upper surface of the proximal wall and another portion disposed within the proximal wall, and a third spike element comprising a portion protruding from an upper surface of the anterior wall or the posterior wall and another portion disposed within the anterior wall or the posterior wall.
 13. The implant of claim 1, wherein the first anti-migration feature comprises a first plurality of ridges and the second anti-migration feature comprises a second plurality of ridges.
 14. The implant of claim 1, wherein the first anti-migration feature is not disposed on at least a portion of the upper surface of the distal wall and the upper surface of the proximal wall.
 15. The implant of claim 1, wherein the second anti-migration feature is not disposed on at least a portion of the lower surface of the distal wall and at least a portion of the lower surface of the proximal wall.
 16. The implant of claim 1, wherein a portion of the upper surface and a portion of the lower surface of the distal wall are angled relative to one another to provide a tapered distal portion.
 17. The implant of claim 1, wherein the first corner radius of curvature and the second corner radius of curvature are the same.
 18. The implant of claim 1, wherein the first corner radius of curvature and the second corner radius of curvature are four times greater than the third corner radius of curvature and the fourth corner radius of curvature.
 19. The implant of claim 18, wherein the first corner radius of curvature and the second corner radius of curvature are approximately ¼ inch and the third corner radius of curvature and the fourth corner radius of curvature are approximately 1/16 inch.
 20. The implant of claim 1, wherein the first length is less than the second length.
 21. The implant of claim 1, wherein the proximal end and the distal end are angled to converge towards each other in the direction of the anterior wall. 